As stated above, the example given was S18E14, which in the 0-indexed xmltv_ns is 17.13.0.

From the XMLTV DTD:

xmltv_ns: This is intended to be a general way to number episodes and

parts of multi-part episodes. It is three numbers separated by dots,

the first is the series or season, the second the episode number

within that series, and the third the part number, if the programme is

part of a two-parter. All these numbers are indexed from zero, and

they can be given in the form 'X/Y' to show series X out of Y series

made, or episode X out of Y episodes in this series, or part X of a

Y-part episode. If any of these aren't known they can be omitted.

You can put spaces whereever you like to make things easier to read.

(NB 'part number' is not used when a whole programme is split in two

for purely scheduling reasons; it's intended for cases where there

really is a 'Part One' and 'Part Two'. The format doesn't currently

have a way to represent a whole programme that happens to be split

across two or more timeslots.)

Some examples will make things clearer. The first episode of the

second series is '1.0.0/1' . If it were a two-part episode, then the

first half would be '1.0.0/2' and the second half '1.0.1/2'. If you

know that an episode is from the first season, but you don't know

which episode it is or whether it is part of a multiparter, you could

give the episode-num as '0..'. Here the second and third numbers have

been omitted. If you know that this is the first part of a three-part

episode, which is the last episode of the first series of thirteen,

its number would be '0 . 12/13 . 0/3'. The series number is just '0'

because you don't know how many series there are in total - perhaps

the show is still being made!